JP-A No. 128118/1997 discloses a switch which transmits open/close status via wireless transmission. JP-A No. 306188/2000 discloses a sensor which detects pressure based on the change in characteristics of a bridge circuit having a resistance film, and converts the change to a digital form to be transmitted via wireless transmission. JP-A No. 014572/2003 discloses a sensor which detects pressure by a piezoelectric element, and transmits the detected pressure value via wireless transmission. JP-A No. 150771/1993 discloses a technology wherein a pressure sensor is mounted at the tip of a groove, the sensor transmits a signal representing the pressure of each finger to a wireless device via a signal line, and the wireless device transmits the signal via wireless transmission. JP-A No. 228042/2001 discloses a technology wherein a signal from a pressure sensor module is transmitted via wireless transmission.